This invention relates to processes of coating particulate materials.
It is known to provide a pharmaceutical product such as antibiotics and other forms of pills with a coating of some type, e.g., enteric coatings so that the medicine may pass through the stomach and treat the lower intestines and bowel, and other sparingly soluble coatings to allow for controlled and delayed release of the drug into the body. It is also known to coat carbon particles, for medical applications. Yuichi Mori et al "Permeability of heparinized hydrophilic polymer (HRDS): Application to semipermeable membrane for microencapsulation of activated carbon" J. biomedical Material Research, Vol. 16, 27-30, 1982; Chang T. M. S. "Hemoperfusion over microencapsulated absorbent in a patient with hepatic coma", Lancet, ii, 1371-1372, 1972; and Chang T. M. S., Espinosa-Melendaz, E., Francoeur, T. E. and Eade, N. R. "Albumin-collodion activated coated charcoal hemoperfusion in the treatment of severe theophylline intoxication in a 3-year old patent" Pediatric, 65, 811-814, 1980 relate to carbon encapsulation for medical purposes.
Fluidized bed systems have previously been used to coat particles as disclosed in Canadian Pat. Nos. 1,049,334 (Worts et al); 808,109 (Kaltenbach); 754,504 (Grass et al); 544,029 (Tadema et al); and 797,153 (Lindolf et al). These systems generally have the disadvantages of providing non-uniform coatings of unpredictable thickness and of providing an unsatisfactory level of particle agglomeration.
Canadian Pat. No. 795,279 (Heiser) describes a system wherein a high velocity jet is applied to a bed of particles to create an asymmetrical zone of moving particles. A nozzle to apply coating solution to the particles is located below the particle bed and thus may not only contact particles in the moving particle zone. Product particles obtained from this system would be unevenly coated and would probably still have a high degree of agglomeration.